1. Field of the Invention
The present invention relates to recording systems and more particularly to tape recording systems which record sporadically received messages. Still more particularly, the present invention relates to multitrack tape systems which can simultaneously record a plurality of audio messages and which includes means for logging the audio messages for later retrieval and playback.
2. Description of the Prior Art
Multitrack tape recording systems which can simultaneously record a number of audio messages such as telephone messages are well known in the art. Such systems are typically used in environments in which a record is kept of telephone calls received and multiple calls may be received at the same time, such as police departments or fire departments. Typically, the operator who receives the messages will mark down the time at which each message is received in order to have a record of all calls. In order to playback a message, it is desirable to have some means of conveniently locating the desired message from among all of the recorded messages.
Recording systems of the type described above may employ standard audio cassettes as the recording medium. In prior art systems, digital codes indicating the time are continuously recorded on a data track separate from the tracks upon which the audio messages are recorded. When it is desired to play a message which was recorded at a particular time, the digital code corresponding to that time is searched for while the tape is moved at high speed. Once the selected digital code is located, the tape is stopped and the corresponding message played back. A primary disadvantage of such a system is that it requires an extra data track on the tape, thus reducing the width of each data track and reducing the signal to noise ratio of the system.
Another disadvantage of prior art systems in which a time code is continuously recorded is that a portion of the message may not be played back if the time which was logged for the receipt of the call was incorrect. For example, assume the message was recorded beginning in the minute of 12:55 and ending in the minute of 12:59. Assuming that the handwritten log generated in conjunction with the logging system designated the message start time at 12:56, the search would locate the digital code corresponding to 12:56 and begin playing the tape at that point. Thus, several seconds of the message will not be played.
Typically, a tape system is run in a high speed fast forward or rewind mode when searching for a previously recorded message. In order to achieve the fastest winding time, the drive motors for the tape spools are driven at their maximum possible rate. As the tape winds from one hub to another, the linear tape speed with respect to the magnetic heads of the system will vary. In order to accurately read the digital time code from the tape, the data rate of the time code must therefore be determined. Prior art systems have included very elaborate means for determining the data rate of the digital codes in variable speed systems.